A liquid crystal display (LCD) displays an image by adjusting light transmittance of a liquid crystal screen using an electric field. Such a liquid crystal display is divided into a horizontal electric field applying type liquid crystal display and a vertical electric field applying type liquid crystal display.
The vertical electric field applying type liquid crystal display enables the liquid crystal display of a TN (Twisted Nematic) mode to be driven by a vertical electric field formed between a common electrode and a pixel electrode disposed to be opposite to upper and lower substrates. The vertical electric field applying type liquid crystal display has an advantage that an opening ratio is large, but has a disadvantage that a viewing angle is narrow as about 90°.
The horizontal electric field applying type liquid crystal display enables the liquid crystal display of an in plane switch (hereinafter referred to as ‘IPS’) mode to be driven by a horizontal electric field formed between a common electrode and a pixel electrode disposed on a lower substrate in a line. The horizontal electric field applying type liquid crystal display has an advantage that a viewing angle is wide as about 160°, but has a disadvantage that an opening ratio and transmittance are low.
In order to improve such a disadvantage of the horizontal electric field applying type liquid crystal display, a fringe field switch (hereinafter referred to as “FFS”) type liquid crystal display operated by a fringe field has been suggested. The FFS type liquid crystal display has a common electrode and a pixel electrode in each pixel region with an insulator film provided between the common electrode and the pixel electrode, wherein a distance between the common electrode and the pixel electrode is formed to be narrower than a distance between upper and lower substrates so that a fringe field can be formed. Furthermore, liquid crystal molecules filled into a gap between the upper and lower substrate are operated by the fringe field so that an opening ratio and transmittance can be improved.
In general, a capacitive touch sensor is formed at an upper portion of the liquid crystal display formed as described above. This is because, in terms of the principle of the touch sensor, the size of a capacitance formed between a user's finger and a sensing electrode reduces as a distance with a portion in contact with the user's finger increases, and thus a difference in voltages resulting from contact with the user's finger and non-contact with the user's finger is not large. Also, even though the size of the capacitance increases according to an increase in an area of a sensing electrode, when the touch sensor and a liquid crystal display driving part are formed at a lower portion of the liquid display, there is a limitation in sufficiently securing the area of the sensing electrode of the touch sensor.
That is, according to the conventional art, since the liquid crystal display and the capacitive touch sensor are formed on the lower and lower substrates, respectively, it is problematic in that a production process is complicated, a production cost is high, and the touch sensor is easily damaged by an external environment.